alesis qx49 problem

firs, hi-im benleo a hiphop producer.if this post is in the wrong forum im sorry, im new around here.ok-so i bought the qx49 a few month ago.this is a really good keyboard and i love it very much.ever since i bought it had a problem.after a while of playing with it it just stop sending midi signs(i use live 8).its still on, and work fine-the midi sign just disapeard.if i want it to work again, i need to close abelton, turn off the keyboard and then getr in abelton.i thought the problem was in my computer, but a few days ago i went to my freind with it and the same happend(he also use ableton).i use the usb cable.thanks for your help1